Ground based global navigation satellite augmentation systems may be required to employ Ionosphere Gradient Monitors (IGMs) at their ground stations to identify delay gradients caused by extreme changes in the electron density of the ionosphere. An example of one such IGM is described in U.S. Pat. No. 8,094,064 entitled “Ground-Based System and Method to Monitor For Excessive Delay Gradients”, herein incorporated by reference in its entirety and referred to herein as the “'064 patent”. In summary the IGM produces an alert signal or exclusion command telling the ground station to stop using or exclude a certain navigation satellite when the IGM detects that satellite exceeded a threshold.
One problem that exists is that other environmental conditions can sometimes trip an IGM causing excessive alerts in the form of false IGM alarms. For example, in some locations heat-induced tropospheric turbulence in the proximity of a ground station can interfere with a reference receiver, causing a false IGM alarm. False IGM alarms cause the ground station to exclude a satellite even though the satellite signal is still usable.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for improved systems and methods to monitor for false alarms from ionosphere gradient monitors.